The interest is a particular percentage of the amount that initially borrowed amount. simply it can be said as the "costs to borrow money". The amount that the lender gives or the borrower gets is called as the Principal amount. Interest is calculated based on the principle amount and this interest amount differs from place to place.
Interest is calculated as
Where
p is the principal
r is the rate of interest
t is the time
This interest amount is the profit for the lender.